Department of Electrical Engineering

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

We report a detailed study of the structural and magnetic properties of Ni80Cr20 fine particles prepared by physical methods, such as mechanical alloying, wire explosion process (WEP), and chemical methods like sodium borohydride reduction, polyol method. From the analysis of structural and microstructural data, phase formation with the desired composition is confirmed in the particles prepared by the WEP. A comparative study of magnetization data of bulk and nanoparticles of Ni80Cr20 suggests that a weak magnetic moment develops in nanoparticles due to finite-size effects. Analysis of magnetization data suggests a superparamagnetic (SPM) behavior in the smallest sized (34 nm) particles prepared by WEP, while nanoparticles prepared by other methods show ferromagnetic ground state. Further, it is shown that the origin of weak magnetic moment and development of SPM state in the nanoparticles is due to uncompensated surface spins with a negligible interaction effect. © 2021 Elsevier Ltd

World University root node

Department Of Physics

Materials Research Bulletin

Anomalous magnetic behavior in Ni80Cr20 nanoparticles prepared by physical and chemical methods

Silicone insulators are gaining its importance in the transmission and distribution of the power system networks. This study proposes a simple and high throughput way of fabrication of superhydrophobic silicone surfaces. The Nd:YAG nanosecond pulse laser was used to engrave six different types of structures on silicone rubber. The water contact angle (CA) and contact angle hysteresis (CAH) were measured using drop shape analyser goniometer. The self-cleaning property of the structured silicone surfaces was tested. Among six types of patterns, the structures formed through 50% scanning overlapped possess high CA (159 ± 1°) with very low CAH (3°) which is desirable for any self-cleaning surface. However, a completely irradiated silicone surface gives the highest CA (163 ± 2°) with very high CAH (61.84°). The proposed work is a vital step towards making a superhydrophobic insulator surface without the use of any coating for high voltage power system applications. © 2020 Institute of Materials, Minerals and Mining Published by Taylor & Francis on behalf of the Institute.

Surface Engineering

Fabrication of self-cleaning superhydrophobic silicone rubber insulator through laser texturing

a-axis (100) oriented Aluminium Nitride (AlN) favours transverse acoustic wave applications. We have been able to realize preferential (100) oriented AlN films on Molybdenum (Mo) coated Si substrate using reactive RF magnetron sputtering. X-ray diffraction and Fourier-transform infrared spectroscopy studies reveal the crystallinity, preferred orientation and bond formation between Al and N2. Al 2p subpeak at 73.8 eV and N 1s subpeak at 396.6 eV from X-ray photoelectron spectroscopy studies confirm the Al-N and N-Al formation in wurtzite hexagonal phase. From the fabricated Mo-AlN-Mo capacitors, the measured dielectric constant and electrical resistivity were ( 18) and ( 7.5 × 106 Ω.m) respectively. The piezoelectric coefficient d33(eff) of AlN film was ( 4.5) pmV−1. These excellent properties of preferential (100) AlN/Mo films will be very useful for high frequency resonator and energy harvesting applications. © 2021 Elsevier B.V.

Applied Surface Science

Realization of preferential (100) oriented AlN thin films on Mo coated Si substrate using reactive RF magnetron sputtering

We significantly improve the physical understanding and theoretical estimate of the contact resistance of a side-bonded contact to heavily doped semiconductor nanowire by highlighting the edge effects. The contact can be made of metal or metal silicide. Prior model of a side-bonded contact to semiconductor nanowire (NW) estimates the contact resistance using radial tunneling in the contacted NW region, neglecting the edge tunneling and fringing field in the non-contacted NW region. Using realistic TCAD simulations, we show that: (i) edge tunneling dominates over radial tunneling as contact thickness, nanowire radius or ambient dielectric constant are reduced; hence a thin contact together with a low-k surrounding dielectric can yield a significantly lower contact resistance; (ii) fringing field reduces both radial tunneling and edge tunneling. © 2021 Elsevier B.V.

Physica E: Low-Dimensional Systems and Nanostructures

Edge effects on the contact resistance of side-bonded contacts to heavily n-doped silicon nanowires

The problem of multihypothesis testing with controlled sensing of observations is considered. The distribution of observations collected under each control is assumed to follow a single-parameter exponential family distribution. The goal is to design a policy to find the true hypothesis with minimum expected delay while ensuring that the probability of error is below a given constraint. The decision-maker can reduce the delay by intelligently choosing the control for observation collection in each time slot. A policy for this problem is derived that satisfies given constraints on the error probability, and it is shown that this policy is asymptotically optimal in the sense that it asymptotically achieves an information-theoretic lower bound on the expected delay. Numerical results are provided that illustrate an application of the policy to medical diagnostic inference. © 2021 Taylor & Francis Group, LLC.

Fulltext

Sequential Analysis

Sequential controlled sensing for composite multihypothesis testing

Non-invasive evaluation of vascular stiffness has established utility in cardiovascular risk and stroke prediction. This work presents an accelerometric sensor-based system with an integrated hydrostatic pressure correction unit for arterial luminal diameter measurement and local vascular stiffness assessment. A custom-designed accelerometric patch for continuous monitoring of percutaneous acceleration plethysmogram (APG) from the common carotid artery, which could estimate the arterial wall displacement, was developed. A calibration model was established to estimate the true carotid luminal diameter waveform from the accelerometer-based arterial wall displacement signals. The system's accuracy for carotid stiffness measurement was validated by multiple in-vivo human subject studies and compared against a clinical-grade B-mode ultrasound imaging system. Accelerometric-derived carotid diameter waveform morphologically replicated the anachrotic, and dicrotic limb of the true carotid diameter recorded using reference devices. The group-average baseline value of measured carotid end-diastolic diameter and distension was 5.81 ± 0.53 mm and 0.51 ± 0.15 mm with a maximum observed beat-by-beat variation of 6.5% and 9%, respectively. Accelerometer-based vascular stiffness measures showed a significant correlation (R2 > 0.88, P < 0.0001), and clinically acceptable agreement with a reference standard imaging system. APG derived carotid stiffness indices demonstrated the capability to detect expected age-associated changes in stiffness. The study revealed that the accelerometric sensor system offers a reliable, cost-effective method for long-term non-invasive monitoring of location-specific vascular stiffness measures with potential applications in ambulatory healthcare monitors. © 2001-2012 IEEE.

IEEE Sensors Journal

An Accelerometric Sensor System with Integrated Hydrostatic Pressure Correction to Assess Carotid Arterial Stiffness

We study a nonparametric search problem to detect ˚evision L anomalous streams from a finite set of <formula><tex>$S$</tex></formula> data streams. The ˚evisionL anomalous streams are real-valued independent and identically distributed (i.i.d.) sequences drawn from the distribution <formula><tex>$q$</tex></formula>, while the remaining <formula><tex>$S-L$</tex></formula> data streams are i.i.d. sequences drawn from the distribution p. The distributions p and <formula><tex>$q$</tex></formula> are assumed to be \em arbitrary and \em unknown, but distinct. We consider two cases: one where <formula><tex>$L = 1$</tex></formula>, and the other where <formula><tex>$0 \le L \le A$</tex></formula>. In both cases, we propose universal distribution-free sequential tests that are consistent. For the first case, we also: (1) show that the test is universally exponentially consistent and stops in finite time almost surely, and (2) bound the limiting growth rate of the expected stopping time as the probability of error decreases to zero. Simulations show that the performance of the proposed test is better than that of the fixed sample size test. IEEE

IEEE Signal Processing Letters

Sequential Nonparametric Detection of Anomalous Data Streams

In this work, the effects of physical dimensions such as length, width and thickness as well as the mode of vibration and the number of anchors on the performance of longitudinal thin film piezoelectric on silicon (TPoS) MEMS resonators have been studied. TPoS resonators, designed for a resonant frequency of around 1 GHz, were fabricated with a 4 mask CMOS compatible process. A 225 μm wide resonator excited in its 23^rd order had an unloaded quality factor of 9453 (in vacuum), which is the highest value reported so far for similar resonators, motional resistance of 107 Ω and linear thermal coefficient of frequency of -28.4 ppm. We have also studied and modeled the different loss mechanisms in these devices. The model matches well with measured results for resonators of different geometries, modes of vibrations and number of anchors. [2020-0397] IEEE

Journal of Microelectromechanical Systems

Design, Modeling and Fabrication of TPoS MEMS Resonators With Improved Performance at 1 GHz

Life expectancy of a thermally aged oil impregnated pressboard (OIP) in the presence of corrosive dibenzyl disulphide (DBDS) is studied in this work using a fast estimation method based on level of diffusion of Cu contaminant. Data from laser induced breakdown spectroscopy (LIBS) is used as the degradation parameter. Thermogravimetric analysis (TGA) is used for rapid evaluation of life expectancy at various temperatures. Aged OIP material is tested for its surface flashover breakdown strength and its thermal stability is studied by TGA and differential scanning calorimetry. Thermal activation energy is estimated using Flynn-Wall-Ozawa method and is agreement with isothermally calculated values. Aging law is derived and found to be nearly first order based on which temperature dependent life expectancy law is formulated. LIBS data of OIP collected from a failed transformer is considered to be end-of-life condition. Estimated life expectancy values using proposed fast method are compared with traditional long-aging evaluation and are in good agreement. Increase in corrosive DBDS concentration and change in aging medium using proposed method and are found to have a significant impact on life expectancy of the OIP insulation. © 1994-2012 IEEE.

Department of Engineering Design

IEEE Transactions on Dielectrics and Electrical Insulation

Life Expectancy Estimation of Thermally Aged Cu Contaminant-Diffused Oil Impregnated Pressboard

Cupric oxide (CuO) nanostructure arrays have been extensively investigated for solar energy harvesting, electrochemical energy storage, chemical sensing, field-effect transistors, etc. Although most of these applications depend on the collective behavior of an array of such structures, analysis of electrical transport in a single nanostructure, which are the building blocks, is essential for understanding both the fundamental aspects and device performance. Here we report the electrical conduction mechanism in thermally grown single CuO nanowire (NW), which reveals that the current density has an anomalous dependence on the diameter of the NWs - decreasing with an increase in diameter. An analysis of the electrical behavior at room temperature shows that the current density in CuO NWs has different slopes in different regions of the applied bias indicating distinct types of charge transport, which are characterized as near Ohmic (lower voltage), trap controlled, and space charge limited conduction (higher applied voltage). Further, the trap density and activation energy are calculated from the temperature-dependent current density data, which shows higher values (9.38 × 1015cm-3, 79.4 meV) in thicker NWs compared to that in the thinner ones (3.96 × 1015 cm-3, 63.9 meV). Investigation of the NWs with Raman and photoluminescence spectra establishes the presence of Cu2O phase in thicker NWs, which act as hole traps to hinder the charge transport in p-type CuO and resulting in lower conductivity at higher diameters. This study helps to design and fabricate prototype nanodevices with desired conductivity based on CuO NWs. © 2021 IOP Publishing Ltd.